I. Introduction to Crane Interlock Protection Devices
Crane interlock protection devices play a crucial role in ensuring the safety and proper operation of cranes. These devices are designed to prevent certain actions or movements of the crane’s mechanisms when specific conditions are not met, thereby avoiding potential accidents and ensuring the well-being of the operators and the surrounding environment. There are several types of interlock protection devices based on different parts and operations of the crane, each with its own specific working principle.
II. Interlock Protection between the Boom Support Stopper and the Boom Luffing Mechanism
Function and Purpose An interlock protection device should be installed between the boom support stopper and the boom luffing mechanism. The main purpose of this interlock is to ensure that the luffing mechanism cannot be activated before the support stopper has its supporting function removed. This is of great significance as it prevents any unexpected movement of the boom during the transition when the support is being adjusted or removed.
Working Principle The interlock protection device typically consists of a series of mechanical and electrical components that work together to achieve the interlocking function. For example, there may be a mechanical linkage that physically blocks the operation of the luffing mechanism when the support stopper is in its supporting position. This mechanical blockage could be in the form of a lever or a latch that engages with the moving parts of the luffing mechanism, preventing it from rotating or moving in the direction required for luffing.
In addition to the mechanical aspect, there is often an electrical interlock as well. Sensors are installed on the support stopper to detect its position. When the support stopper is in place and providing support, these sensors send a signal to the control system of the crane. The control system is programmed to receive this signal and, based on it, disable the electrical circuit that powers the luffing mechanism. This means that even if an operator were to attempt to activate the luffing mechanism through the control panel, the electrical power would not be supplied to the relevant motors or actuators, and thus the luffing action could not occur.
Only when the support stopper is properly withdrawn and its position change is detected by the sensors (which then send a new signal to the control system indicating that the support has been removed), will the control system enable the electrical circuit for the luffing mechanism. At this point, the luffing mechanism can be safely operated, ensuring that there is no risk of the boom moving unexpectedly while the support is being adjusted.
III. Interlock Protection for Crane Doors (Bridge and Gantry Cranes)
Function and Purpose For bridge cranes and gantry cranes, interlock protection devices should be installed on the doors that provide access to the crane (such as the entry doors) and on the hatch doors through which the operator ascends to the bridge from the driver’s cab. The purpose of these interlocks is to ensure that the crane’s running mechanism cannot be activated when these doors are open. This is crucial as it prevents the crane from moving while there may be people entering or exiting the crane or in the process of climbing onto the bridge, thereby avoiding potential collisions or other accidents.
Working Principle Similar to the previous interlock, these door interlocks also involve a combination of mechanical and electrical components. On the mechanical side, there are usually latches or locking mechanisms on the doors themselves. When the door is closed, these latches engage with corresponding parts on the crane structure, ensuring a proper seal and also providing a mechanical indication that the door is in the correct position.
Electrically, sensors are installed on the doors to detect their open or closed status. When the door is opened, the sensors send a signal to the crane’s control system. The control system is designed to receive this signal and, upon detecting that a door is open, immediately cut off the power supply to the running mechanism of the crane. This means that the motors that drive the wheels or other components responsible for the crane’s movement along its rails or on the ground will not receive electrical power, and thus the crane will remain stationary.
Conversely, when the door is closed and the sensors detect this change in status (sending a new signal to the control system), the control system will restore the power supply to the running mechanism, allowing the crane to be operated normally again. This way, the safety of anyone in the vicinity of the doors or on the crane is ensured, as the crane will not move unexpectedly while the doors are open.
IV. Interlock Protection for the Entrance to the Driver’s Cab (When Located on a Moving Part)
Function and Purpose When the driver’s cab is located on a moving part of the crane, an interlock protection device should be installed at the entrance to the cab. The purpose of this interlock is to ensure that the crane’s running mechanism cannot be activated when the door of the entrance to the cab is open. This is necessary to prevent the crane from moving while the operator is entering or exiting the cab, which could lead to serious accidents such as the operator being thrown off or caught between moving parts.
Working Principle The working principle of this interlock protection device is also based on a combination of mechanical and electrical components. Mechanically, there are usually locking mechanisms on the cab entrance door that engage with the surrounding structure when the door is closed, providing a secure closure and a physical indication that the door is in the proper state.
Electrically, sensors are installed on the cab entrance door to detect its open or closed status. When the door is opened, the sensors send a signal to the crane’s control system. The control system, upon receiving this signal, immediately cuts off the power supply to the running mechanism of the crane. This ensures that the motors that drive the movement of the crane will not receive electrical power, and thus the crane will remain stationary while the operator is entering or exiting the cab.
Once the door is closed again and the sensors detect this change in status (sending a new signal to the control system), the control system will restore the power supply to the running mechanism, allowing the crane to be operated normally once more. This interlock protection device provides an important safeguard for the safety of the operator during the process of entering and exiting the cab while the crane is in operation.
In conclusion, crane interlock protection devices work through a combination of mechanical and electrical components to ensure that specific crane mechanisms are disabled when certain safety-critical conditions are not met. These devices are essential for maintaining the safety of crane operations, protecting the operators, and preventing potential accidents that could occur due to unexpected movements of the crane while people are in vulnerable positions such as entering or exiting the crane or adjusting support mechanisms.
